1. Field of the Invention
The invention concerns a method of applying a coating product, especially a powder paint fused by heat; it is more particularly concerned with an improvement which makes it possible to reduce the time needed to change the coating product, usually to change the color of the coating product, which is applied by electrostatic means.
The invention is also concerned with an installation for implementing this method.
2. Description of the Prior Art
It is known that the main problem in applying powder paint fused by heat arises from the relatively lengthy operation needed to change the color. The powder is conventionally applied by electrostatic means within a booth the pressure inside which is slightly reduced by suction. The suction means are advantageously associated with powder recovery means in the form of a centrifugal separator, for example, usually known as a "cyclone" and the clean air outlet from which is coupled to a final filter separating out powder particles recovered by the separator, before the air is returned to the atmosphere. Until now each color change has entailed cleaning the booth and the suction means. The most serious problems and greatest loss of time arise mainly from cleaning the booth. The powder recovered in the separator is generally recycled. It is therefore necessary to clean very carefully all the surfaces on which powder may be deposited whenever the nature and/or the color of the powder is changed, so that the parts are never sprayed with a mixture of different color powders. The sprayers, storage tanks and feed pipes can easily be cleaned or changed. Cleaning the filter system and in particular the separator generally does not raise any problems and can be done quickly. On the other hand, when it comes to the spray booth there has yet to be found a totally satisfactory solution to the problem of removing all traces of powder from the walls of the booth. One known solution is described in PCT application No 87-00771. According to this document the booth essentially consists of four plastics material film walls defining a sort of tunnel supported by rollers and an internal framework. Each time the color is changed the plastics material films are paid out between the rollers and the framework to provide a clean internal surface. However, the internal framework has to be cleaned by hand before the plastics material films are paid out and while the films are moving the framework may become soiled again by the powder deposited on the walls, which can constitute a source of pollution of the clean walls. This solution is therefore not fully satisfactory and moreover it uses complex mechanical devices. Also, the operation is costly because of the non-negligible consumption of plastics material film and it is difficult to implement.
The invention proposes a more economical solution that is very quick to use.
The invention arises from the observation that it is virtually impossible to prevent by any simple means the deposition of some of the sprayed powder onto the inside walls of the enclosure and that any cleaning of the walls requires lengthy intervention (which therefore renders the installation unusable for a long time) and its results are somewhat uncertain. The basic idea of the invention is therefore purely and simply to remove the enclosure each time the coating product is changed and to replace it with another corresponding to the new coating product. There is therefore provided a plurality of interchangeable enclosures the number of which corresponds to the number of different coating products to be applied. Multiple sets of such enclosures can also be provided, suited to different objects.